Two meteotsunamis formed on Lake Michigan on one single day last month and thanks to a handy NOAA animation, we not only know that it happened but how they actually formed.

For those wondering exactly what a meteotsunami is, the National Oceanic and Atmospheric Administration defines them as "large waves that scientists are just beginning to better understand."

Tsunamis are triggered by seismic activity while meteotsunamis are created through air-pressure changes and disturbances during "fast-moving" weather events. Some meteotsunamis have been recorded as high as 6-feet high, and have been spotted in the Great Lakes, Gulf of Mexico, and off the coasts of the Atlantic Ocean, Mediterranean and Adriatic seas.

Back on April 13 (Friday the 13th for those keeping track), NOAA's Great Lakes Environmental Research Laboratory reports that thunderstorms created the duo of meteotsunamis. "Short, extreme bursts of wind and pressure" were said to be the specific cause that resulted in a sudden spike of water levels near Ludington.

Update: model output is here! Check out this GIF of not one, but TWO meteotsunamis that came across the lake on Friday the 13th. Red = higher water level, blue = lower. pic.twitter.com/zjTZXRquNA

Ludington is where NOAA says one of the meteotsunamis submerged a breakwater and water levels quickly rose by about 1.51 feet. Head about 25 miles north to Manistee, and this is where some docks were reported as damaged by the changing water levels of Lake Michigan.

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NOAA's Great Lakes-based research lab broke the formation of the two meteotsunamis down in the below animation:

You may have seen [?] of the meteotsunami that hit Ludington Friday. It's a big deal! They're rare, and it's even rarer to capture photos. A seiche developed later, after the meteotsunami. But they aren't the same thing! So, we present to you...SEICHES VS METEOTSUNAMIS: A THREAD

Check out these charts of winds and pressure from that day. The meteotsunami was caused by those short, extreme bursts of wind and pressure. After the meteotsunami, you can see the slow buildup of pressure and the continued winds - those set us up for a weekend of seiche-ing. pic.twitter.com/Ta1VSy28D3

According to the Great Lakes Environmental Research Laboratory, about 100 meteotsunamis are spotted on the Great Lakes each year but most are on the smaller size.

The Weather Channel reported that talks of meteotsunamis went into great detail at the American Geophysical Union Conference back in February. Eric Anderson, of NOAA's Great Lakes Environmental Research Laboratory, said that thunderstorms are responsible for about 80 percent of meteotsunamis on the Great Lakes.

Most of these weather events occur during the late-spring and summer months in the Great Lakes, and that the most recent deadly meteotsunami was blamed for the death of seven people on July, 4, 2003 in Sawyer, Michigan.

"Identifying a meteotsunami is a challenge because its characteristics are almost indistinguishable from a seismic tsunami," NOAA reports on its website. "It can also be confused with wind-driven storm surge or a seiche. These uncertainties make it difficult to predict a meteotsunami and warn the public of a potential event.

"However, NOAA scientists have identified atmospheric conditions that are likely to generate a meteotsunami and continue to work on ways to forecast them."